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Urease Activity on a Clay-Organic Complex¹

ABSTRACT

Urease may be adsorbed on hexadecyltrimethyl-ammonium (HDTMA)-smectite by hydrophobic bonding. This mechanism is independent of pH and results in enzyme activity ash igh as that in homogenous solution. As much as forty percent by weight of enzyme can be bound to the clay-organic complex before free enzyme appears in the supernatant solution. Several cycles of washing the enzyme-clay-organic complex at the 10% by weight level did not result in any enzyme removal. The free and bound enzyme behaved similarly with respect to kinetic parameters, pH optimum, and selectivity for substrate. Thermal stability and resistance to proteolysis were greatly decreased for urease immobilized on HDTMA smectite as compared with homogenous solution. In soils, enzymes may be immobilized on natural clay-organic matter complexes by hydrophobic bonding.

¹ Journal Article no. 11522 of the Michigan Agric. Exp. Stn. East Lansing.

² Assistant Professor and Professor, respectively. Dep. of Crop & Soil Sciences, Michigan State Univ., East Lansing, Michigan, 48824.

Received for publication July 23, 1984. Accepted for publication December 14, 1984.